In a system or network carrying AC current, the current, as measured at any particular point in the system, may lead, or lag, the voltage measured at the same point by some phase difference. To the extent to which current and voltage are out of phase, the system may be said to be carrying reactive power at that point, in addition to real (or true) power, P, which is the product of the voltage and in-phase component of the current carried at a specified point in the system. Reactive power is the product of the voltage and quadrature component of the current, and is commonly designated by the letter Q, as it will be herein. Reactive power delivery to the load of a system, within specified limits, is crucial to the maintenance of voltage control, owing to the fact that loads may contain significant non-ohmic components, and thus impose reactive power demands on the system. Reactive power issues are discussed at length in Principles for Efficient and Reliable Reactive Power Supply and Consumption, Federal Energy Regulatory Commission Staff Report (2005), which is incorporated herein by reference.